Tidy up OSCConnectionDelegate's dispatch_queue_t
Serialise accesses to OSCConnection's pendingPackets on one queue
Add -[OSCMessage isEqual:] for other OSCMessages
Fix -[OSCMessage lengthOfArgumentAtIndex:] for strings

I wasn't padding the string to 4-byte alignments so all subsequent offsets were wrong.
Implement OSCMessage.arguments for more basic types
Block -[OSCConnection disconnect…] when clearing packet queue

There is a race condition when clearing the pending packets asynchronously, as this might be done from within a dealloc—the OSCConnection might be gone by the time the block is dispatched.